1. Field of the Invention
The present invention relates to a novel crystalline 2-(1-isopropoxycarbonyloxy-2-methylpropyl)-7,8-dimethoxy-4(5H),10-dioxo-2H-1,2,3-triazolo[4,5-c][1]benzazepine which is useful as medicaments.
2. Background Art
2-(1-Isopropoxycarbonyloxy-2-methylpropyl)-7,8-dimethoxy-4(5H),10-dioxo-2H-1,2,3-triazolo[4,5-c][1]benzazepine (hereinafter referred to as “compound A”) is a compound, represented by the following chemical structural formula, which is expected to be utilized as an antiallergic agent, as described in WO 99/16770 (Japanese Patent No. 3188482 and U.S. Pat. No. 6,372,735) (the disclosure of each of these publications is incorporated herein by reference). 
The product obtained by the method described in the above publications, is a light yellow powder which is low in compound A purity as determined based on percentage area obtained by HPLC analysis. The product is estimated to be a mixture of compound A with its decomposition product(s) and analogs and the like.
In the production of medicaments, constantly providing a compound having an identical quality is necessary for constantly providing given activity and effect. Therefore, in order to ensure the even quality which is required in a starting material for the production of medicaments as well as the given activity and effect thereof, a pure compound should be constantly produced. Furthermore, stable crystals, which can maintain the same quality, are also desired from the viewpoint of good storage stability.